The effect of amalgam exposure on mercury- and antibiotic-resistant bacteria

Peri-implantitis is not periodontitis: Scientific discoveries shed light on microbiome-biomaterial interactions that may determine disease phenotype

Peri-implantitis is an immune-mediated biological complication that is attributed to bacterial biofilms on the implant surface. As both periodontitis and peri-implantitis have similar inflammatory phenotypes when assessed cross-sectionally, treatment protocols for peri-implantitis were modeled according to those used for periodontitis. However, lack of efficacy of antimicrobial treatments targeting periodontal pathogens coupled with recent discoveries from open-ended microbial investigation studies create a heightened need to revisit the pathogenesis of peri-implantitis compared with that of periodontitis. The tale of biofilm formation on intraoral solid surfaces begins with pellicle formation, which supports initial bacterial adhesion. The differences between implant- and tooth-bound biofilms appear as early as bacterial adhesion commences. The electrostatic forces and ionic bonding that drive initial bacterial adhesion are fundamentally different in the presence of titanium dioxide or other implant alloys vs mineralized organic hydroxyapatite, respectively. Moreover, the interaction between metal surfaces and the oral environment leads to the release of implant degradation products into the peri-implant sulcus, which exposes the microbiota to increased environmental stress and may alter immune responses to bacteria. Clinically, biofilms found in peri-implantitis are resistant to beta-lactam antibiotics, which are effective against periodontal communities even as monotherapies and demonstrate a composition different from that of biofilms found in periodontitis; these facts strongly suggest that a new model of peri-implant infection is required.

The impact of amalgam dental fillings on the frequency of Helicobacter pylori infection and H. pylori eradication rates in patients treated with concomitant, quadruple, and levofloxacin-based therapies

BACKGROUND AND AIM

Mercury exposure is encountered most commonly in individuals with amalgam fillings. The toxic, bactericidal, and immunosuppressive effects of mercury are well known. Furthermore, multiple antibiotic resistance can be transferred, together with mercury resistance. The aim of this study was to investigate the frequency of Helicobacter pylori infection in dyspeptic patients with amalgam fillings and the effect of the amalgam fillings on H. pylori eradication rates in these patients.

PATIENTS AND METHODS

Four hundred and seventy-five patients who presented with dyspeptic complaints and underwent upper gastrointestinal endoscopy and gastric biopsy were included in this study. One hundred and sixty-nine (35.6%) patients were negative and 306 (64.4%) patients were positive for H. pylori. All of the participants underwent dental examinations in a blinded manner. The participants were divided into two groups on the basis of the presence of amalgam fillings. The H. pylori-positive patients were divided randomly into three subgroups: patients who received concomitant therapy (CT) (rabeprazole-amoxicillin-clarithromycin-metronidazole for 14 days; n=122); patients who received quadruple therapy (QT) (rabeprazole-tetracycline-metronidazole-colloidal bismuth subcitrate for 10 days; n=97); and patients who received levofloxacin-based therapy (LT) (rabeprazole-amoxicillin-levofloxacin for 10 days; n=87). Eradication success was detected by a urea breath test 6 weeks after the end of treatment.

RESULTS

The frequency of H. pylori infection was significantly lower in the filling group compared with the nonfilling group (53.7 and 78.8%, respectively; P<0.001). The eradication rates in the CT, QT, and LT groups were 65.5, 67.0, and 58.6%, respectively, in the intention-to-treat (ITT) analysis and 69.6, 70.7, and 62.2%, respectively, in the per-protocol (PP) analysis. In all of the H. pylori-positive patients and separately in the CT and LT groups, the eradication rates were significantly lower in the filling group compared with the nonfilling group. However, in the QT group, there was no significant difference between the patients with and without fillings (P=0.001, 0.003, 0.012, 0.14, respectively). Logistic regression analysis showed that the absence of amalgam filling exerts independent effects on the increased frequency of H. pylori infection and increased rate of H. pylori eradication.

CONCLUSION

This is the first study to show a lower frequency of H. pylori colonization in patients with amalgam fillings than without and that H. pylori eradication rates are lower in patients with amalgam fillings compared to those without.

Recent Advances in Mercury Research

Mercury (Hg) is a highly toxic, non-essential, naturally occurring metal with a variety of uses. Mercury is not required for any known biological process and its presence in the human body may be detrimental, especially to the nervous system. Both genetic and behavioral studies suggest that mercury levels, age (both of exposure and at testing), and genetic background determine disease processes and outcome. The metal receptors and genes responsible for mercury metabolism also appear to play a pivotal role in the etiology of mercury-induced pathology. This review presents information about the latest advances in mercury research, with particular focus on low-level exposures and the contribution of genetics to toxic outcome. Future studies should address the contribution of genetics and low-level mercury exposure to disease, namely gene x environment interactions, taking into consideration age of exposure as developing animals are exquisitely more sensitive to this metal. In addition to recent advances in understanding the pathology associated with mercury exposure, the review highlights transport mechanisms, cellular distribution and detoxification of mercury species in the body.

Mechanisms and Modifiers of Methylmercury-Induced Neurotoxicity

The neurotoxic consequences of methylmercury (MeHg) exposure have long been known, however a complete understanding of the mechanisms underlying this toxicity is elusive. Recent epidemiological and experimental studies have provided many mechanistic insights, particularly into the contribution of genetic and environmental factors that interact with MeHg to modify toxicity. This review will outline cellular processes directly and indirectly affected by MeHg, including oxidative stress, cellular signaling and gene expression, and discuss genetic, environmental and nutritional factors capable of modifying MeHg toxicity.

Biofilm Formation on Dental Restorative and Implant Materials

Biomaterials for the restoration of oral function are prone to biofilm formation, affecting oral health. Oral bacteria adhere to hydrophobic and hydrophilic surfaces, but due to fluctuating shear, little biofilm accumulates on hydrophobic surfaces in vivo. More biofilm accumulates on rough than on smooth surfaces. Oral biofilms mostly consist of multiple bacterial strains, but Candida species are found on acrylic dentures. Biofilms on gold and amalgam in vivo are thick and fully covering, but barely viable. Biofilms on ceramics are thin and highly viable. Biofilms on composites and glass-ionomer cements cause surface deterioration, which enhances biofilm formation again. Residual monomer release from composites influences biofilm growth in vitro, but effects in vivo are less pronounced, probably due to the large volume of saliva into which compounds are released and its continuous refreshment. Similarly, conflicting results have been reported on effects of fluoride release from glass-ionomer cements. Finally, biomaterial-associated infection of implants and devices elsewhere in the body is compared with oral biofilm formation. Biomaterial modifications to discourage biofilm formation on implants and devices are critically discussed for possible applications in dentistry. It is concluded that, for dental applications, antimicrobial coatings killing bacteria upon contact are more promising than antimicrobial-releasing coatings.

Is exposure to mercury a driving force for the carriage of antibiotic resistance genes?

The mercury resistance gene merA has often been found together with antibiotic resistance genes in human commensal Escherichia coli. To study this further, we analysed mercury resistance in collections of strains from various populations with different levels of mercury exposure and various levels of antibiotic resistance. The first population lived in France and had no known mercury exposure. The second lived in French Guyana and included a group of Wayampi Amerindians with a known high exposure to mercury. Carriage rates of mercury resistance were assessed by measuring the MIC and by detecting the merA gene. Mercury-resistant E. coli was found significantly more frequently in the populations that had the highest carriage rates of antibiotic-resistant E. coli and in parallel antibiotic resistance was higher in the population living in an environment with a high exposure to mercury, suggesting a possible co-selection. Exposure to mercury might be a specific driving force for the acquisition and maintenance of mobile antibiotic resistance gene carriage in the absence of antibiotic selective pressure.

Growing oral biofilms in a constant depth film fermentor (CDFF)

In order to grow organisms in such a manner as to mimic their physiological growth state in vivo, it is often desirable to grow them as biofilms in the laboratory. There are numerous systems available to accomplish this; however, some are more suited to the growth of oral biofilms (dental plaque) than others. The operating parameters of one such model, the constant depth film fermentor (CDFF), are given in this unit. This model is particularly suited to studying the varied biofilms which exist in the oral cavity because environmental factors such as the substratum, nutrient source, and gas flow can be altered.

The withdrawal of antimicrobial treatment as a mechanism for defeating resistant microorganisms

Antimicrobial resistance is a major concern in health care and farming settings throughout the world. The level of antimicrobial resistance continues to increase and the requirement for a novel and possibly dramatic change in therapy choices is required. One possible mechanism for overcoming resistance is the actual removal of antimicrobial treatment from the therapeutic armoury. This review examines the potential for success of a policy advocating the reduction of antimicrobial use and additionally the withdrawal of such treatments. Evidence from agriculture suggests that the removal of certain drugs from animal husbandry can result in concomitant falls in certain drug resistances in human patients.